The Mechanistic Basis for Photobiomodulation Therapy of Neuropathic Pain by Near Infrared Laser Light

High-power laser photobiomodulation therapy for immediate pain relief of refractory oral mucositis

PURPOSE

We aimed to evaluate the efficacy of high-power (class IV) laser photobiomodulation (PBM) therapy for immediate pain relief due to oral mucositis (OM) refractory to recommended first-line therapy.

METHODS

This retrospective study included 25 cancer patients with refractory chemotherapy- or radiotherapy-induced OM (16 and 9 patients, respectively) that were treated for pain relief with an intraoral InGaAsP diode laser (power density = 1.4 W/cm2). Pain was self-assessed immediately before and after laser treatment using a 0-to-10 numeric rating scale ([NRS], "0" = no pain, "10" = intolerable pain).

RESULTS

Patients reported an immediate decrease in pain following 94% (74 of 79) of the PBM sessions, in 61% (48 sessions) the pain reduction was over 50%, and in 35% (28 sessions) the initial pain was completely eliminated. There were no reports of increased pain post-PBM. For chemotherapy and radiotherapy-treated patients, mean reduction in pain NRS post-PBM was 4.8 ± 2.5 (p < 0.001) and 4.5 ± 2.8 (p = 0.001), indicating a post-PBM reduction of 72% and 60% of the initial pain level, respectively. The analgesic benefit of PBM remained for a mean of 6.0 ± 5.1 days. One patient reported a transient burning sensation after one PBM session.

CONCLUSIONS

High-power laser PBM may provide nonpharmacologic, patient-friendly, long-lasting, rapid pain relief for refractory OM.

The mitochondrial-related effect of the 905 nm photobiomodulation therapy on 50B11 sensory neurons

Photobiomodulation therapy (PBMT) is known as a complementary tool to alleviate pain sensation in patients, nevertheless, there is still a gap of knowledge on its mechanism of action, thus limiting its clinical employment. In this study, a possible molecular mechanism of the 905 nm PBMT (0.25 W/cm2 ; 3, 6, 12, and 18 J/cm2 , 5 Hz) analgesic effect was tested on 50B11 cells, by investigating its impact on mitochondria. A decrement of adenosine triphosphate was detected, moreover, an increment of total reactive oxygen species and mitochondrial superoxide anion was found after PBMT with all protocols tested. PBMT at 18 J diminished the mitochondrial membrane potential, and influenced mitochondrial respiration, decreasing the oxygen consumption rate. Finally, a decrement of extracellular signal-regulated kinase 1/2 phosphorylation was observed with the protocol using 12 J. Taken together these findings highlighted the intracellular effects, mainly correlated to mitochondrial, induced by 905 nm PBMT in sensory neurons, indicating the central role of this organelle in the cellular response to 905 nm near-infrared laser light.

Anti-hyperalgesic effects of photobiomodulation therapy (904 nm) on streptozotocin-induced diabetic neuropathy imply MAPK pathway and calcium dynamics modulation

Several recent studies have established the efficacy of photobiomodulation therapy (PBMT) in painful clinical conditions. Diabetic neuropathy (DN) can be related to activating mitogen-activated protein kinases (MAPK), such as p38, in the peripheral nerve. MAPK pathway is activated in response to extracellular stimuli, including interleukins TNF-α and IL-1β. We verified the pain relief potential of PBMT in streptozotocin (STZ)-induced diabetic neuropathic rats and its influence on the MAPK pathway regulation and calcium (Ca²⁺) dynamics. We then observed that PBMT applied to the L4-L5 dorsal root ganglion (DRG) region reduced the intensity of hyperalgesia, decreased TNF-α and IL-1β levels, and p38-MAPK mRNA expression in DRG of diabetic neuropathic rats. DN induced the activation of phosphorylated p38 (p-38) MAPK co-localized with TRPV1⁺ neurons; PBMT partially prevented p-38 activation. DN was related to an increase of p38-MAPK expression due to proinflammatory interleukins, and the PBMT (904 nm) treatment counteracted this condition. Also, the sensitization of DRG neurons by the hyperglycemic condition demonstrated during the Ca²⁺ dynamics was reduced by PBMT, contributing to its anti-hyperalgesic effects.

Effect Of Low-Level Laser Therapy On Inflammatory Sequеlae Of Impacted Mandibular Third Molar Surgery: A Single-Blind, Placebo-Controlled, Randomized Clinical Trial

Objective — Postoperative pain, facial swelling, and limitation of mouth opening are common sequеlae of lower third molar surgery. The objective of the study was to evaluate the effect of Low- level laser irradiation in controlling these sequеlae. Material and Methods — This randomized, single-blinded, split-mouth pilot study was carried out at the department of oral and maxillofacial surgery, university affiliated hospital, Erbil, Iraq. The study was conducted on 20 patients (13 males and 7 females), with a mean age of 26.3±7.4 years, who needed surgical removal of symmetrical bilateral impacted lower third molars. In each patient, one side was treated by low level laser and the other side was control. Laser irradiation was performed by postoperative single intraoral application of 940 nm laser beam at four points. Pain, trismus, and facial swelling were evaluated at the first, third, and seventh postoperative days. The data were analyzed using Mann–Whitney U test and unpaired t -test. Results — As compared to the control sides, low- level laser irradiated sides showed a significant reduction in visual analogue pain scales (VAS) during the first three postoperative days (P<0.05). The VAS scores of the laser treated sides were 4.46, 4.00, and 3.35 as compared to 6.58, 5.82, and 5.17 for the control sides. The swelling, and trismus were significantly reduced on the first and third postoperative days in the laser treated sides, as compared to the control sides (P<0.05). The facial measurements during the first and third postoperative days were 108.72 mm and 114.77 mm in the laser sides and 113.57 mm and 118.43 mm in the control sides. The degree of mouth opening during the first and third postoperative days were 33.48 mm and 30.37 mm in the laser sides and 27.93 mm and 25.58 mm in the control sides Conclusions — Single intraoral application of low- level laser is effective in reducing pain, swelling and trismus after mandibular third molar surgery. Therefore, it can be used as an adjuvant in controlling postoperative complications after lower third molar surgery.

Near-Infrared Photobiomodulation of Living Cells, Tubulin, and Microtubules In Vitro

We report the results of experimental investigations involving photobiomodulation (PBM) of living cells, tubulin, and microtubules in buffer solutions exposed to near-infrared (NIR) light emitted from an 810 nm LED with a power density of 25 mW/cm² pulsed at a frequency of 10 Hz. In the first group of experiments, we measured changes in the alternating current (AC) ionic conductivity in the 50–100 kHz range of HeLa and U251 cancer cell lines as living cells exposed to PBM for 60 min, and an increased resistance compared to the control cells was observed. In the second group of experiments, we investigated the stability and polymerization of microtubules under exposure to PBM. The protein buffer solution used was a mixture of Britton-Robinson buffer (BRB aka PEM) and microtubule cushion buffer. Exposure of Taxol-stabilized microtubules (~2 μM tubulin) to the LED for 120 min resulted in gradual disassembly of microtubules observed in fluorescence microscopy images. These results were compared to controls where microtubules remained stable. In the third group of experiments, we performed turbidity measurements throughout the tubulin polymerization process to quantify the rate and amount of polymerization for PBM-exposed tubulin vs. unexposed tubulin samples, using tubulin resuspended to final concentrations of ~ 22.7 μM and ~ 45.5 μM in the same buffer solution as before. Compared to the unexposed control samples, absorbance measurement results demonstrated a slower rate and reduced overall amount of polymerization in the less concentrated tubulin samples exposed to PBM for 30 min with the parameters mentioned above. Paradoxically, the opposite effect was observed in the 45.5 μM tubulin samples, demonstrating a remarkable increase in the polymerization rates and total polymer mass achieved after exposure to PBM. These results on the effects of PBM on living cells, tubulin, and microtubules are novel, further validating the modulating effects of PBM and contributing to designing more effective PBM parameters. Finally, potential consequences for the use of PBM in the context of neurodegenerative diseases are discussed.

Effect of photobiomodulation combined with physical therapy on functional performance in children with myelomeningocele: A protocol randomized clinical blind study

INTRODUCTION

Myelomeningocele is a severe type of spina bifida, resulting from improper closure of the neural tube. This condition drastically affects the structures of the spinal cord resulting in deficiencies. The combination of these deficiencies results in an overall decrease in mobility and functional participation amongst this population. Physiotherapy plays an essential role in rehabilitating people with MMC. The current literature shows that resources such as photobiomodulation (PBM) may support the rehabilitation of neurological conditions. The aim of the proposed study is to evaluate the effects of photobiomodulation (PBM) combined with physical therapy on functional performance in children with low lumbosacral myelomeningocele.

MATERIALS AND METHODS

This is a protocol randomized clinical blind study, that will include 30 individuals of both sexes, aged between 5 to 8 years, diagnosed with low and sacral lumbar myelomeningocele and capable of performing the sit-to-stand task. The participants will be randomly assigned into two treatment groups: PBM + physiotherapeutic exercises and sham PBM + physiotherapeutic exercises. Irradiation will be carried out with light emitting diode (LED) at a wavelength of 850 nm, energy of 25 J per point, 50 seconds per point and a power of 200 mW. The same device will be used in the placebo group but will not emit light. Muscle activity will be assessed using a portable electromyograph (BTS Engineering) and the sit-to-stand task will be performed as a measure of functioning. Electrodes will be positioned on the lateral gastrocnemius, tibialis anterior and rectus femoris muscles. The Pediatric Evaluation of Disability Inventory will be used to assess functional independence. Quality of life will be assessed using the Child Health Questionnaire-Parent Form 50. Changes in participation will be assessed using the Participation and Environment Measure for Children and Youth. The data will be analyzed with the aid of GraphPad PRISM.

DISCUSSION

The results of this study can contribute to a better understanding of the effectiveness of PBM on functioning and quality of life in children with myelomeningocele.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT04425330.

Photobiomodulation promotes neural regeneration when compared to simvastatin treatment in a sciatic nerve crush model

To determine whether the effects of photobiomodulation (PBM) were associated with the use of Simvastatin in the functional recovery from sciatic nerve in mice submitted to crush injury. Fifty Swiss mice (approximately 3 months old; average weight 40 g) were randomly divided into six groups: naive, sham, control, PBM (660 nm, 10 J/cm2; 30 mW; 0.6 J per day for 28 days; 0.06 cm2; 16.8 J total and 20 s), Simvastatin (20 mg/kg), and PBM/Simv (association of the two protocols). The sciatic functional index (SFI), thermal heat hyperalgesia, mechanical hyperalgesia, and thermographic evaluation were used as analyses. The evaluations were performed preoperatively and 7, 14, 21, and 28 days after the initial injury analyzed by two-way analysis of variance (ANOVA) for mixed models followed by the Bonferroni post-test. All groups except sham and naive presented an SFI compatible with severe peripheral nerve injury on the 7th day of evaluation. The PBM group presented better results in the SFI analysis (p < 0.001) on the 21st postoperative day compared to the control group. This benefit was maintained when compared to the Simvastatin (p < 0.001) and PBM/Simv groups (p < 0.01). The results of the thermal and mechanical hyperalgesia and thermography analyses were not significant (p > 0.05). The obtained results showed that PBM alone was more effective compared to Simvastatin alone or PBM combined with Simvastatin for sciatic nerve injury in mice.

Mechanisms and Pathways of Pain Photobiomodulation: A Narrative Review

A growing body of evidence supports the modulation of pain by light exposure. As such, phototherapy is being increasingly utilized for the management of a variety of pain conditions. The modes of delivery, and hence applications of phototherapy, vary by wavelength, intensity, and route of exposure. As such, differing mechanisms of action exist depending upon those parameters. Cutaneous application of red light (660 nm) has been shown to reduce pain in neuropathies and complex regional pain syndrome-I, whereas visual application of the same wavelength of red light has been reported to exacerbate migraine headache in patients and lead to the development of functional pain in animal models. Interestingly visual exposure to green light can result in reduction in pain in variety of pain conditions such as migraine and fibromyalgia. Cutaneous application typically requires exposure on the order of minutes, whereas visual application requires exposure on the order of hours. Both routes of exposure elicit changes centrally in the brainstem and spinal cord, and peripherally in the dorsal root ganglia and nociceptors. The mechanisms of photobiomodulation of pain presented in this review provide a foundation in furtherance of exploration of the utility of phototherapy as a tool in the management of pain. PERSPECTIVE: This review synopsizes the pathways and mechanisms through which light modulates pain and the therapeutic utility of different colors and exposure modalities of light on pain. Recent advances in photobiomodulation provide a foundation for understanding this novel treatment for pain on which future translational and clinical studies can build upon.

In vitro effects of photobiomodulation therapy on 50B11 sensory neurons: evaluation of cell metabolism, oxidative stress, mitochondrial membrane potential (MMP), and capsaicin-induced calcium flow

The analgesic properties of photobiomodulation therapy (PBMT) have been raising increasing interest in the clinical community due to the positive effects observed on patients, nevertheless the mechanistic basis of its action on peripheral sensory neurons remains still elusive. In this study, the effect of near-infrared (NIR) PBMT at 800 and 970 nm of wavelength was investigated on the 50B11 immortalized nociceptive sensory neuronal cell line by evaluating capsaicin-induced calcium flow and different markers correlated to mitochondria, that is, ATP, reactive oxygen species (ROS), and mitochondrial membrane potential (MMP). Calcium peak stimulated by capsaicin, the ligand of TRPV1 channel, was decreased in neurons pre-irradiated with the combination of the two wavelengths. Furthermore, delivering the 800 and 970 nm separately an increment of ATP, as well as MMP hyperpolarization were detected; notably, the 800 nm wavelength also increased ROS and O₂^- levels. Our findings, obtained on an in vitro model of nociception, show the positive effect of PBMT on two potential photo-targets of NIR light, namely the TRPV1 channel and the mitochondria.

Effects of Chronic Photobiomodulation with Transcranial Near-Infrared Laser on Brain Metabolomics of Young and Aged Rats

Since laser photobiomodulation has been found to enhance brain energy metabolism and cognition, we conducted the first metabolomics study to systematically analyze the metabolites modified by brain photobiomodulation. Aging is often accompanied by cognitive decline and susceptibility to neurodegeneration, including deficits in brain energy metabolism and increased susceptibility of nerve cells to oxidative stress. Changes in oxidative stress and energetic homeostasis increase neuronal vulnerability, as observed in diseases related to brain aging. We evaluated and compared the cortical and hippocampal metabolic pathways of young (4 months old) and aged (20 months old) control rats with those of rats exposed to transcranial near-infrared laser over 58 consecutive days. Statistical analyses of the brain metabolomics data indicated that chronic transcranial photobiomodulation (1) significantly enhances the metabolic pathways of young rats, particularly for excitatory neurotransmission and oxidative metabolism, and (2) restores the altered metabolic pathways of aged rats towards levels found in younger rats, mainly in the cerebral cortex. These novel metabolomics findings may help complement other laser-induced neurocognitive, neuroprotective, anti-inflammatory, and antioxidant effects described in the literature.

Effectiveness of Low-Level Laser Irradiation in Reducing Pain and Accelerating Socket Healing After Undisturbed Tooth Extraction

Introduction: This study aimed to determine the effect of low-level laser therapy (LLLT) on reducing complications following tooth extraction. Methods: This randomized clinical trial consisted of 40 subjects who underwent lower molar extraction. The patients were randomly assigned to 4 groups. Group 1 was irradiated with a 660 nm laser (200 mW, 30 seconds radiation to lingual, buccal and occlusal surfaces of the socket, 6 J/area). In group 2, an 810 nm laser was applied similar to group 1. In group 3, a combination of 660 and 810 nm lasers was used. The patients in group 4 served as a placebo group. LLLT was performed after 0.5-1 hour of extraction and 2 days later. The participants were asked to record pain degree using a visual analogue scale (VAS) over 7 days. The amount of wound healing was evaluated on the third and seventh days. Results: There was no significant difference in pain scores among the groups at any of the assessment intervals (P >0.05). The between-group differences in wound healing scores were small and insignificant (P >0.05). Conclusion: LLLT with 660 nm or 810 nm lasers or their combination had no greater effect than the placebo laser for reducing the complications of tooth extraction.

"Photobiomics": Can Light, Including Photobiomodulation, Alter the Microbiome?

Objective: The objective of this review is to consider the dual effects of microbiome and photobiomodulation (PBM) on human health and to suggest a relationship between these two as a novel mechanism. Background: PBM describes the use of low levels of visible or near-infrared (NIR) light to heal and stimulate tissue, and to relieve pain and inflammation. In recent years, PBM has been applied to the head as an investigative approach to treat diverse brain diseases such as stroke, traumatic brain injury (TBI), Alzheimer's and Parkinson's diseases, and psychiatric disorders. Also, in recent years, increasing attention has been paid to the total microbial population that colonizes the human body, chiefly in the gut and the mouth, called the microbiome. It is known that the composition and health of the gut microbiome affects many diseases related to metabolism, obesity, cardiovascular disorders, autoimmunity, and even brain disorders. Materials and methods: A literature search was conducted for published reports on the effect of light on the microbiome. Results: Recent work by our research group has demonstrated that PBM (red and NIR light) delivered to the abdomen in mice, can alter the gut microbiome in a potentially beneficial way. This has also now been demonstrated in human subjects. Conclusions: In consideration of the known effects of PBM on metabolomics, and the now demonstrated effects of PBM on the microbiome, as well as other effects of light on the microbiome, including modulating circadian rhythms, the present perspective introduces a new term "photobiomics" and looks forward to the application of PBM to influence the microbiome in humans. Some mechanisms by which this phenomenon might occur are considered.

Cognitive Enhancement by Transcranial Photobiomodulation Is Associated With Cerebrovascular Oxygenation of the Prefrontal Cortex

Transcranial infrared laser stimulation (TILS) is a novel, safe, non-invasive method of brain photobiomodulation. Laser stimulation of the human prefrontal cortex causes cognitive enhancement. To investigate the hemodynamic effects in prefrontal cortex by which this cognitive enhancement occurs, we used functional near-infrared spectroscopy (fNIRS), which is a safe, non-invasive method of monitoring hemodynamics. We measured concentration changes in oxygenated and deoxygenated hemoglobin, total hemoglobin and differential effects in 18 healthy adults during sustained attention and working memory performance, before and after laser of the right prefrontal cortex. We also measured 16 sham controls without photobiomodulation. fNIRS revealed large effects on prefrontal oxygenation during cognitive enhancement post-laser and provided the first demonstration that cognitive enhancement by transcranial photobiomodulation is associated with cerebrovascular oxygenation of the prefrontal cortex. Sham control data served to rule out that the laser effects were due to pre-post task repetition or other non-specific effects. A laser-fNIRS combination may be useful to stimulate and monitor cerebrovascular oxygenation associated with neurocognitive enhancement in healthy individuals and in those with prefrontal hypometabolism, such as in cognitive aging, dementia and many neuropsychiatric disorders.

Analgesic effect of Photobiomodulation Therapy: An in vitro and in vivo study

Laser therapy, also known as Photobiomodulation (PBM) is indicated to reduce pain associated with different pathologies and applied using protocols that vary in wavelength, irradiance and fluence. Its mechanisms of action are still unclear and possibly able to directly impact on pain transmission, reducing nociceptor response. In our study, we examined the effect of two specific laser wavelengths, 800 and 970 nm, extensively applied in the clinical context and known to exert important analgesic effects. Our results point to mitochondria as the primary target of laser light in isolated dorsal root ganglion (DRG) neurons, reducing adenosine triphosphate content and increasing reactive oxygen species levels. Specifically, the 800 nm laser wavelength induced mitochondrial dysregulation, that is, increased superoxide generation and mitochondrial membrane potential. When DRG neurons were firstly illuminated by the different laser protocols and then stimulated with the natural transient receptor potential cation channel subfamily V member 1 (TRPV1) ligand capsaicin, only the 970 nm wavelength reduced the calcium response, in both amplitude and frequency. Consistent results were obtained in vivo in mice, by subcutaneous injection of capsaicin. Our findings demonstrate that the effect of PBM depends on the wavelength used, with 800 nm light mainly acting on mitochondrial metabolism and 970 nm light on nociceptive signal transmission.

miR-202 modulates the progression of neuropathic pain through targeting RAP1A

Neuropathic pain is a somatosensory disorder which is caused by disease or nerve injury that affects the nervous system. microRNAs (miRNAs) are proved to play crucial roles in the development of neuropathic pain. However, the role of miR-202 in neuropathic pain is still unknown. Sprague-Dawley rats were used for constructing the neuropathic pain model. The expression of miR-202 was determined by quantitative real-time polymerase chain reaction. Potential target gene for miR-202 was measured using bioinformatics methods and Western blot analysis. In this study, we used rats to establish a neuropathic pain model and measured the effect of miR-202 in neuropathic pain. We demonstrated that miR-202 expression was downregulated in the spinal dorsal horn of bilateral sciatic nerve chronic constriction injury (bCCI) rat. However, miR-202 expression was not changed in the dorsal root ganglion, hippocampus, and anterior cingulated cortex of bCCI rat. We identified that RAP1A was a direct target gene of miR-202 in the PC12 cell. RAP1A expression was upregulated in the spinal dorsal horn of bCCI rat. Overexpression of miR-202 could improve the pain threshold for bCCI rats in both hindpaws, indicating that miR-202 overexpression could lighten the pain threshold for model rats. Moreover, RAP1A overexpression increased the pain threshold effect of miR-202 overexpression treated bCCI rats, indicating that miR-202 could lighten the pain threshold through inhibiting RAP1A expression. These data suggested that miR-202 acted pivotal roles in the development of neuropathic pain partly through targeting RAP1A gene.

Low-level laser therapy modulates demyelination in mice

There are no effective therapies for remyelination. Low-level laser therapy (LLLT) has been found advantageous in neurogenesis promotion, cell death prevention, and modulation of inflammation in central and peripheral nervous system models. The purpose of this study was to analyse LLLT effects on cuprizone-induced demyelination. Mice were randomly distributed into three groups: Control Laser (CTL), Cuprizone (CPZ), and Cuprizone Laser (CPZL). Mice from CPZ and CPZL groups were exposed to a 0.2% cuprizone oral diet for four complete weeks. Six sessions of transcranial laser irradiation were applied on three consecutive days, during the third and fourth weeks, with parameters of 36 J/cm², 50 mW, 0.028 cm² spot area, continuous wave, 1 J, 20 s, 1.78 W/cm² in a single point equidistant between the eyes and ears of CTL and CPZL mice. Motor coordination was assessed by the rotarod test. Twenty-four hours after the last laser session, all animals were euthanized, and brains were extracted. Serum was obtained for lactate dehydrogenase toxicity testing. Histomorphological analyses consisted of Luxol Fast Blue staining and immunohistochemistry. The results showed that laser-treated animals presented motor performance improvement, attenuation of demyelination, increased number of oligodendrocyte precursor cells, modulated microglial and astrocytes activation, and a milder toxicity by cuprizone. Although further studies are required, it is suggested that LLLT represents a feasible therapy for demyelinating diseases.

Perspective on Broad-Acting Clinical Physiological Effects of Photobiomodulation

Research into photobiomodulation reveals beneficial effects of light therapy for a rapidly expanding list of medical conditions and illnesses. Although it has become more widely accepted by the mainstream medicine, the effects and mechanisms of action appear to be poorly understood. The therapeutic benefits of photobiomodulation using low-energy red lasers extend far beyond superficial applications, with a well-described physics allowing an understanding of how red lasers of certain optimum intensities may cross the cranium. We now have a model for explaining potential therapeusis for applications in functional neurology that include stroke, traumatic brain injury, and neurodegenerative conditions in addition to the currently approved functions in lipolysis, in onychomycosis treatment, and in pain management.

Low-level ultrahigh-frequency and ultrashort-pulse blue laser irradiation enhances osteoblast extracellular calcification by upregulating proliferation and differentiation via transient receptor potential vanilloid 1

BACKGROUND AND OBJECTIVE

Low-level laser irradiation (LLLI) exerts various biostimulative effects, including promotion of wound healing and bone formation; however, few studies have examined biostimulation using blue lasers. The purpose of this study was to investigate the effects of low-level ultrahigh-frequency (UHF) and ultrashort-pulse (USP) blue laser irradiation on osteoblasts.

STUDY DESIGN/ MATERIALS AND METHODS

The MC3T3-E1 osteoblast cell line was used in this study. Following LLLI with a 405 nm newly developed UHF-USP blue laser (80 MHz, 100 fs), osteoblast proliferation, and alkaline phosphatase (ALP) activity were assessed. In addition, mRNA levels of the osteoblast differentiation markers, runt-related transcription factor 2 (Runx2), osterix (Osx), alkaline phosphatase (Alp), and osteopontin (Opn) was evaluated, and extracellular calcification was quantified. To clarify the involvement of transient receptor potential (TRP) channels in LLLI-induced biostimulation, cells were treated prior to LLLI with capsazepine (CPZ), a selective inhibitor of TRP vanilloid 1 (TRPV1), and subsequent proliferation and ALP activity were measured.

RESULTS

LLLI with the 405 nm UHF-USP blue laser significantly enhanced cell proliferation and ALP activity, compared with the non-irradiated control and LLLI using continuous-wave mode, without significant temperature elevation. LLLI promoted osteoblast proliferation in a dose-dependent manner up to 9.4 J/cm² and significantly accelerated cell proliferation in in vitro wound healing assay. ALP activity was significantly enhanced at doses up to 5.6 J/cm² , and expression of Osx and Alp mRNAs was significantly increased compared to that of the control on days 3 and 7 following LLLI at 5.6 J/cm² . The extent of extracellular calcification was also significantly higher as a result of LLLI 3 weeks after the treatment. Measurement of TRPV1 protein expression on 0, 3, and 7 days post-irradiation revealed no differences between the LLLI and control groups; however, promotion of cell proliferation and ALP activity by LLLI was significantly inhibited by CPZ.

CONCLUSION

LLLI with a 405 nm UHF-USP blue laser enhances extracellular calcification of osteoblasts by upregulating proliferation and differentiation via TRPV1. Lasers Surg. Med. 50:340-352, 2018. © 2017 Wiley Periodicals, Inc.

Photobiomodulation of human dermal fibroblasts in vitro: decisive role of cell culture conditions and treatment protocols on experimental outcome

Photobiomodulation-based (LLLT) therapies show tantalizing promise for treatment of skin diseases. Confidence in this approach is blighted however by lamentable inconsistency in published experimental designs, and so complicates interpretation. Here we interrogate the appropriateness of a range of previously-reported treatment parameters, including light wavelength, irradiance and radiant exposure, as well as cell culture conditions (e.g., serum concentration, cell confluency, medium refreshment, direct/indirect treatment, oxygen concentration, etc.), in primary cultures of normal human dermal fibroblasts exposed to visible and near infra-red (NIR) light. Apart from irradiance, all study parameters impacted significantly on fibroblast metabolic activity. Moreover, when cells were grown at atmospheric O2 levels (i.e. 20%) short wavelength light inhibited cell metabolism, while negligible effects were seen with long visible and NIR wavelength. By contrast, NIR stimulated cells when exposed to dermal tissue oxygen levels (approx. 2%). The impact of culture conditions was further seen when inhibitory effects of short wavelength light were reduced with increasing serum concentration and cell confluency. We conclude that a significant source of problematic interpretations in photobiomodulation reports derives from poor optimization of study design. Further development of this field using in vitro/ex vivo models should embrace significant standardization of study design, ideally within a design-of-experiment setting.